Titration topics

Question

Write your answers in the space provided.

1. A burette was filled to the 0.00 mL mark with a standard 0.10 M KOH solution. This volume was recorded in the table of results. Then, 10.00 mL of nitric acid were pipetted into an Erlenmyer flask. A drop of indicator was added to the acid. No colour change was observed. The KOH solution from the burette was gently let out and the acid was continuously swirled until the first permanent pink colour was detected - at this point the stopcock of the burette was immediately closed and the burette reading was noted. This procedure was repeated three more times.

What was the objective of this activity?

1. The student did not record the name of the indicator that was added to the acid in the Erlenmeyer flask. Which indicator was added to the flask?

1. The following table of results was obtained from the student’s lab book. Complete the table by filling in the volume of KOH that was delivered from the burette for each trial.

Titrating 0.10 M KOH(aq) with 10.00 mL ____M HNO_3(aq)

Trials	1	2	3	4
Final buret reading NaOH (0.01mL)	12.75	23.15	39.40	13.65
Initial buret reading NaOH (0.01mL)	0.00	13.25	27.45	3.75
Volume NaOH delivered (mL)

1. For calculation purposes, what is the average volume of potassium hydroxide that was delivered from the burette?

1. Calculate the number of moles of potassium hydroxide that was used in the titration.

1. Write a balanced molecular equation, with state symbols, for the reaction between potassium hydroxide and nitric acid.

1. Write the net ionic equation for the reaction between potassium hydroxide and nitric acid.

1. Based on the answers for e and f, state the number of moles of acid that was used in the titration.

1. Calculate the concentration of the nitric acid used in this titration.

1. Can you use copper(II) hydroxide instead of potassium hydroxide in this titration? Explain.

1. Using ionization equations, explain what is meant by ‘nitric acid is a strong acid but acetic acid is a weak acid’.

Answer 1

Apparently this is a homework assignment for a chem. lab. Wyzant does not condone tutors doing homework, but I will try to guide you through this so that you can provide the answers yourself.

The objective of the activity is to find the molarity of the nitric acid using the method of titration.

Which indicator was used? There are several that could have been used. (Hint: Look up phenolphthalein and see if that might have been used for titration of a strong acid with a strong base).

To fill in the last row of the table, simply subtract the initial reading from the final reading to get mls KOH.

Take the average of the 4 trials to get the average mls of KOH used.

To calculate moles of KOH, used the average mls and convert to liters by dividing by 1000. Then multiply that value by the molarity (moles/L) of the KOH (0.10 M). This gives you moles KOH used.

Balanced equation is KOH(aq) + HNO3(aq) ==> KNO3(aq) + H2O(l)

Net ionic equation is H+(aq) + OH-(aq) ==> H2O(l)

Moles of acid in titration = same as moles of KOH since it is a 1:1 mole ratio in the balanced equation

Concentration of nitric acid (HNO3) = moles HNO3 / Liters of HNO3 solution

Can you use copper(II) hydroxide? Not really. Why? Because it has negligible solubility in water.

What is meant by strong acid vs weak acid? A strong acid is one that ionized/dissociates completely. A weak acid only ionizes/dissociates partially. For nitric acid (strong acid) and acetic acid (weak acid), we have:

HNO3 (nitric acid; strong acid) ==> H+(aq) + NO3-(aq) 100% ionized

CH3COOH (acetic acid; weak acid) ==> H+(aq) + CH3COO-(aq) Less than 100% ionized. Extent ionization is given by the Ka for the weak acid.